The Astrophysical Formation of Asymmetric Molecules and the Emergence of a Chiral Bias

The biomolecular homochirality in living organisms has been investigated for decades, but its origin remains poorly understood. It has been shown that circular polarized light (CPL) and other energy sources are capable of inducing small enantiomeric excesses (ees) in some primary biomolecules, such as amino acids or sugars. Since the first findings of amino acids in carbonaceous meteorites, a scenario in which essential chiral biomolecules originate in space and are delivered by celestial bodies has arisen. Numerous studies have thus focused on their detection, identification, and enantiomeric excess calculations in extraterrestrial matrices. In this review we summarize the discoveries in amino acids, sugars, and organophosphorus compounds in meteorites, comets, and laboratory-simulated interstellar ices. Based on available analytical data, we also discuss their interactions with CPL in the ultraviolet (UV) and vacuum ultraviolet (VUV) regions, their abiotic chiral or achiral synthesis, and their enantiomeric distribution. Without doubt, further laboratory investigations and upcoming space missions are required to shed more light on our potential extraterrestrial molecular origins.

Influence of crystallization on formation of biomolecular homochirality on Earth

A mathematical model of coupled autocatalytic reactions along with crystallization of diastereomers was considered. It was shown that the differences in the physical properties of diastereomers could be a 100% enantioselective factor, which makes it possible to obtain a significant chiral polarization even at low enantioselectivity of autocatalysis. It was shown that molecules, which are more complex, should have higher chiral polarization than simpler ones. The calculation of the dynamics of the model under consideration shows that the presence of binomial coefficients in the reaction of pair formation from two different enantiomers leads to the occurrence of an additional 100% enantioselective factor even in case when diastereomers have identical properties. Estimates show that theoretical difference between right and left-handed molecules (which is due to weak interaction), is sufficient to explain directed symmetry breaking and construction of biological molecules from L-amino acids and D-sugars at the origin of life on Earth. It is shown that such a model constitutes an amplifier with a feedback. It is proposed that a two-layer system with a feedback could be attributed to the formation of longer homochiral chains, which are necessary for the formation of life on Earth.